A 59-year-old man with a body mass index of 25.2 kg/m² was diagnosed with adenocarcinoma of the descending colon near the splenic flexure and a rectal tumor 5 cm from the anal verge. Totally laparoscopic left hemicolectomy with transrectal natural orifice specimen extraction surgery (NOSES) was performed together with transanal local excision of the rectal lesion. The inferior mesenteric vein was preserved, and the specimen was removed through an approximately 3 cm upper rectal incision using a double-bag technique. Operative time was 140 min and blood loss was 20 mL. Pathology showed moderately differentiated adenocarcinoma of the left colon (pT₃N_1b; 3/14 lymph nodes positive; perineural invasion present; no definite lymphovascular invasion), with an additional tubulovillous adenoma containing focal intramucosal carcinoma in the same specimen. The rectal lesion was a 0-Ip tubulovillous adenoma with focal moderately differentiated adenocarcinoma invading the head of the submucosa (pT₁), with negative margins and no lymphovascular or perineural invasion. The patient was discharged on postoperative day 6 without complications. This case suggests that an integrated transrectal NOSES and transanal local excision strategy may be technically feasible in carefully selected patients with synchronous left-sided colon and rectal cancer.